This invention relates to an intravascular device used in the treatment of aneurysms, and especially in the occlusion of cerebrovascular saccular aneurysms.
Saccular aneurysms occur at the branching of arteries in the body and comprise a sack-like formation of the artery wall which extends outwardly from the bifurcation point between the arterial branches. The aneurysm has a neck forming the juncture with the artery and is capped by a dome. During formation of the aneurysm, the arterial internal elastic lamina disappears at the base of the neck, the sack wall thins and weakens and connective tissue replaces smooth-muscle cells. The aneurysm tends to rupture at the dome and bleeding ensues.
Rupture of a cerebrovascular saccular aneurysm is especially serious due to the associated high mortality rate (10% within the first day of rupture, 25% within three months) and the major neurological deficits experienced by those who survive the initial hemorrhage. Naturally, therapeutic treatment of cerebrovascular aneurysms emphasizes preventing the initial rupture.
Intravascular Catheter Treatment Technique
Intravascular catheter techniques for treating saccular aneurysms are discussed in U.S. Pat. No. 5,122,136, hereby incorporated by reference, and U.S. Pat. No. 6,010,498, also hereby incorporated by reference.
The techniques described in these patents can be summarized with reference to FIGS. 1 and 2, which show a saccular aneurysm 20 formed in an artery 22 at a bifurcation point 24. The treatment techniques involve positioning a catheter 26 at the artery bifurcation point 24, the catheter tip 28 extending partially into the neck 30 of the aneurysm 20. Once the catheter is in position, a length of platinum or platinum alloy wire 32 is snaked through the catheter""s lumen 34 through the aneurysm neck 30 and into the aneurysm 20. The wire 32 has a length of between 0.4 and 20 inches (1 and 50 cm), is relatively thin (between 0.001-0.005 inches in diameter) and flexible and loops and tangles randomly as it is packed into the aneurysm. Blood which would normally circulate under pressure into the aneurysm, causing it to enlarge, weaken and rupture, begins to form clots 36 on the platinum wire tangle and eventually the clots merge and enlarge to form an occlusion 38 (see FIG. 2) which seals off the aneurysm from the blood flow, preventing further enlargement and rupture.
Clotting on the wire 32 within aneurysm 20 is promoted by mechanical and/or electrical means. Forming the wire 32 into a continuous coil having a diameter between 0.010 and 0.020 inches will promote clotting mechanically by providing a multiplicity of adjacent sites on the wire where clots can adhere and join together. Running an electrical current of approximately 0.01 to 2 milliamperes through the wire with the wire forming the anode of the circuit at a positive 0.1 to 6 volts will cause clots to form by the phenomenon of electrothrombosis. Electrothrombosis takes advantage of the fact that white blood cells, red blood cells, platelets and fibrogen are typically negatively charged in blood having normal pH, and these negatively charged components are, therefore, electrostatically attracted to the positively charged wire. The electrostatic attraction of the blood components promotes and speeds the clotting process.
Once the appropriate length of wire is positioned in the aneurysm and the occlusion has been formed, the wire 32 is released at or near the neck 30 of the aneurysm and the catheter is withdrawn (FIG. 2). Wire release is effected by any one of several means, for example, mechanical means or electrolytic means.
Release of the wire by mechanical means involves another wire (not shown) which is attached in tandem with the platinum wire 32. The other wire extends through the catheter and provides the means to push the platinum wire through the catheter and into the aneurysm. The other wire has a spring biased mechanical clasp (not shown) at its end which grips an end 40 of wire 32 (see FIG. 2). The clasp remains engaged with the wire end 40 as long as the clasp remains within the catheter lumen. To release wire 32, the clasp is temporarily extended from the lumen, the spring biasing opens the clasp and the wire end 40 is released. The other wire and the clasp are drawn back into the catheter lumen, which is then removed from the artery.
For release of the wire by electrolytic means, the end 40 of platinum wire 32 is attached to the other wire by a wire segment formed of stainless steel (not shown). When it is desired to release the platinum wire, the stainless steel segment is positioned outside of the catheter lumen and exposed to the blood stream. Application of an electrical current through the exposed stainless steel portion causes it to corrode away, releasing the platinum wire 32.
While this catheter technique holds great promise of effective treatment for preventing aneurysm rupture, especially cerebrovascular saccular aneurysms, it has a significant drawback in that it is not always possible to ensure that the entire length of wire 32 remains within the aneurysm. Even if the entire length of wire is successfully positioned wholly within the aneurysm during the procedure, it has been found that the end 40 of the wire can work its way out of the aneurysm over time, extend through the aneurysm neck 30 and protrude into the artery 22 as illustrated in FIG. 2. Blood flowing through the artery past the wire end will form a clot 36 on the protruding wire end 40, and this clot could separate from the wire end and cause a stroke or embolism. Statistical results predict that as many as 5% of the patients treated by this technique will suffer complications caused by the wire extending through the aneurysm neck and into the artery. Clearly, there is a need for improving this catheter treatment technique to eliminate the potential for embolisms or stroke as a result of the procedure.
The invention comprises a flexible bag adapted to pass through a catheter lumen and expand upon release from the lumen to substantially occupy a fluid-filled cavity larger than the lumen. The bag is adapted to receive fluid within the cavity. The bag also receives a clotting medium which promotes coagulation of the fluid when in contact with it.
The bag comprises a plurality of interlaced flexible filamentary members spaced apart so as to form a multiplicity of pores in the interstices between the interlaced filamentary members. The pores are sized to allow the fluid in the cavity to enter the bag but prevent outward protrusion of the clotting medium from the bag. The filamentary members may comprise, for example, multifilaments such as spun yarns, individual monofilaments, multiple monofilament strands twisted together or any combination thereof.
The filamentary members are resiliently biased to expand the bag to a first diameter substantially filling the cavity upon release from the catheter lumen. Preferably, the filamentary members are themselves resilient and biased to effect the expansion of the bag to the first diameter. Other means for biasing the filamentary members are described below. The filamentary members are also resiliently deformable to a second diameter smaller than the first diameter, the second diameter being sized to slidingly interfit within the catheter lumen.
Preferably, the bag is used in the intravascular treatment of saccular aneurysms, thus, the aforementioned cavity is the saccular aneurysm, the fluid is blood and the clotting medium comprises a length of wire. The wire length could be contained in the bag while positioned in the catheter or fed into the bag after it is positioned in its expanded diameter within the aneurysm. Preferably, the wire is compatible with human tissue and conducts electricity, thus, allowing a current to be passed to promote clotting by electrothrombosis. Platinum is the preferred wire material because it fulfills the necessary requirements.
Preferably, the wire is fed into the bag through an opening in the bag formed for receiving the wire. The filamentary members forming the bag are resiliently biased adjacent to the opening to form a constriction in the bag which closes off the opening and prevents the wire from extending outwardly therethrough. The filamentary members are resiliently deformable away from the opening to expand the constriction and allow access to said bag through the opening to feed the wire.
The filamentary members are preferably interlaced by braiding, as it is well known that braided structures exhibit a xe2x80x9ctrellis effectxe2x80x9d, wherein the braided members rotate and slide relatively to one another when a force is applied. For the braided bag according to the invention, this effect results in radial contraction of the bag with axial expansion and radial expansion upon axial contraction, thus, allowing the bag to be resiliently deformed from the first expanded diameter into the second, smaller diameter by the application of appropriate tensile force to the bag, as described below.
Multifilament polymer yarns, preferably of polyester, are used for the filamentary members. Other feasible materials include, for example, ePTFE, PTFE, PET, nylon, polyethylene, PGA and PLA. The yarn material is chosen for its compatibility with human tissue, as well as mechanical properties such as elongation, strength, flexibility, toughness and resilience. Monofilament yarns are also used, the yarns having a denier between about 5 and 100.
Although numerous geometries could be used to form the bag, it is preferably braided into the form of an elongated tube or sleeve, the opening being formed at an end of the tube. The tubular form provides several advantages, for example, it allows the bag to be produced on a circular braiding machine, the braid angle is uniform and easily controlled, and the diameter and length of the tube can be varied over a wide range of values. The filamentary members at the open end are biased radially inwardly to form the constriction closing off the opening and preventing the wire clotting medium from extending outwardly through the opening once it is positioned within the bag.
It is sometimes desired to provide a second means for biasing the filamentary members and effect expansion of the bag to the first diameter upon release from the catheter lumen. The second means includes providing a plurality of supplemental filamentary members contiguous with the first named filamentary members. The supplemental filamentary members are resiliently biased radially outwardly to expand the bag to the first diameter but are deformable to allow for contraction of the bag to the second diameter sized to fit within the catheter lumen.
Preferably, the supplemental filamentary members are interbraided with the first named filamentary members, although they could also be positioned interiorly or exteriorly of the bag. Supplemental filamentary members positioned on the bag interior will naturally push outwardly against the interlaced filamentary members to expand the bag, whereas supplemental members on the exterior of the bag must be attached to the bag, for example, as with sutures.
It is advantageous to make the supplemental filamentary members from radiopaque monofilament wires. This allows the bag to be viewed by means of fluoroscopy or X-ray techniques when it is positioned within the body. Nitinol, a shape-memory metal, is the preferred material because it is bio-compatible and has outstanding elastic properties such as a relatively high yield stress providing excellent resilience and flexibility.
Biasing of the filamentary members may also be provided by positioning a continuous flexible stent within the bag. Stents are often used in the repair of vascular aneurysms and provide a supporting structure resiliently biased to push radially outwardly to expand the bag to the first diameter. The stent is also resiliently deformable into a collapsed shape sized to slidingly interfit within the catheter lumen along with the bag. Biasing forces within the stent expand it radially outwardly upon release of the stent and the bag from the catheter. In its preferred form, the stent comprises a resilient, flexible wire biased along a helical path conforming to a tubular shape to interfit within the preferred tubular shape of the bag.
A third means for biasing the filamentary members and effect expansion of the bag to the first diameter comprises providing supplemental filamentary members which are elastic and interbraided with one another. The supplemental filamentary members are contiguous with the first named filamentary members forming the bag and are in tension when the bag is deformed to the second diameter. Upon release of the bag from the catheter lumen, the supplemental filamentary members tend to contract, and because they are interbraided, the braid structure tends to expand radially in response to the contraction due to the xe2x80x9ctrellis effectxe2x80x9d characteristic of braided structures. The radial expansion of the interbraided supplemental filamentary members biases the first named filamentary members and expands the bag to the first diameter. Preferably, the first named filamentary members are interlaced by braiding to form the bag and the supplemental filamentary members are interbraided with the first named filamentary members. It is advantageous to distribute the supplemental filamentary members uniformly around the bag to provide for a uniform radial expansion. Elastic yarns such as silicone monofilaments are preferred as the supplemental filamentary members.
The invention also contemplates an assembly of the bag and the catheter ready to be used to treat the aneurysm. The assembly comprises a catheter having a lumen, the bag being in the second, smaller diameter shape and positioned within the lumen, the bag being slidable through the lumen for insertion into the saccular aneurysm.
The invention also includes a method of forming a flexible bag defining an enclosed space and adapted to fit within a catheter lumen and expand to substantially occupy a blood-filled saccular vascular aneurysm. The enclosed space is adapted to receive the blood and a clotting medium, for example, a length of wire, for promoting clotting. The preferred method of forming the bag comprises the steps of:
(a) braiding a plurality of flexible resilient filamentary members into a resiliently deformable tube of predetermined length and predetermined first diameter sized to substantially fill the aneurysm, the tube having open ends oppositely arranged;
(b) biasing the filamentary members into a first shape state substantially maintaining the tube in a radially expanded shape at the first diameter, the filamentary members being resiliently deformable into a second shape state wherein the tube is collapsed to a second diameter smaller than the first and sized to slidingly interfit within the catheter lumen;
(c) biasing the filamentary members radially inwardly at the ends to form constrictions substantially closing off the ends, the filamentary members being resiliently deformable radially outwardly of the tube providing an opening for access to the enclosed space within the bag for receiving the clotting medium therein.
Preferably, the braiding step is performed over a mandrel having a bulbous shape in order to help establish the biasing of the filamentary members into the expanded first diameter as well as the constrictions closing off the open ends of the tube. The biasing step is conveniently performed by applying heat to the filamentary members while the filamentary members are on the mandrel, thereby fixing the biased shape.
When it is desired to use supplemental filamentary members to augment the extension and/or support of the bag, further method steps are included such as:
(d) interbraiding a plurality of radiopaque monofilament wires with the filamentary members forming the tube; and
(e) biasing the wires into the first shape state, the wires being resiliently deformable into the second shape state.
As previously mentioned, the radiopaque wires are resiliently collapsible to the second diameter to interfit within the catheter lumen. The wires push radially outwardly to support the bag when the bag expands to the first diameter upon release from the catheter.
When the embodiment according to the invention includes the catheter, the method also includes the step of positioning the bag within the lumen of the catheter, the bag being collapsed to the second, smaller diameter to slidingly interfit within the lumen.
It is an object of the invention to provide a bag useful in the treatment of vascular saccular aneurysms.
It is another object of the invention to provide a bag insertable into a vascular saccular aneurysm.
It is another object of the invention to provide a bag which can be used to contain a clotting medium, the bag serving to prevent undesired blood clots from forming in the vascular system but to promote blood clot formation in the aneurysm.
It is yet another object of the invention to provide a bag which is resiliently deformable between two shape states, one of which is expanded to substantially fill the saccular aneurysm, the other of which is collapsed to slidingly interfit within a catheter lumen for insertion into the aneurysm.
It is still another object of the invention to provide a bag resiliently biased to nominally assume the expanded shape state.
It is again another object of the invention to provide a means for augmenting the expansion and support of the bag in the expanded shape state.
It is yet again another object of the invention to provide a bag which holds a clotting medium comprising a wire used for electrothrombosis within a saccular vascular aneurysm.
It is still another object of the invention to provide a bag which is self expanding to said expanded shape state upon release from the catheter lumen.
These and other objects of the invention can be discerned from a consideration of the following drawings and detailed description of the invention.